How PyArmor Does It

Look at what happened after is obfuscated by PyArmor. Here are the files list in the output path dist:

pytransform/, or _pytransform.dll in Windows, _pytransform.dylib in MacOS

dist/ is obfuscated script, the content is:

from pytransform import pyarmor_runtime
__pyarmor__(__name__, __file__, b'\x06\x0f...')

There is an extra folder pytransform called Runtime Package, which are the only required to run or import obfuscated scripts. So long as this package is in any Python Path, the obfuscated script dist/ can be used as normal Python script. That is to say:

The original python scripts can be replaced with obfuscated scripts seamlessly.

How to Obfuscate Python Scripts

How to obfuscate python scripts by PyArmor?

First compile python script to code object:

char *filename = "";
char *source = read_file( filename );
PyCodeObject *co = Py_CompileString( source, "<frozen foo>", Py_file_input );

Then change code object as the following way

  • Wrap byte code co_code within a try...finally block:

    wrap header:
            LOAD_GLOBALS    N (__armor_enter__)     N = length of co_consts
            CALL_FUNCTION   0
            SETUP_FINALLY   X (jump to wrap footer) X = size of original byte code
    changed original byte code:
            Increase oparg of each absolute jump instruction by the size of wrap header
            Obfuscate original byte code
    wrap footer:
            LOAD_GLOBALS    N + 1 (__armor_exit__)
            CALL_FUNCTION   0
  • Append function names __armor_enter, __armor_exit__ to co_consts

  • Increase co_stacksize by 2

  • Set CO_OBFUSCAED (0x80000000) flag in co_flags

  • Change all code objects in the co_consts recursively

Next serializing reformed code object and obfuscate it to protect constants and literal strings:

char *string_code = marshal.dumps( co );
char *obfuscated_code = obfuscate_algorithm( string_code  );

Finally generate obfuscated script:

sprintf( buf, "__pyarmor__(__name__, __file__, b'%s')", obfuscated_code );
save_file( "dist/", buf );

The obfuscated script is a normal Python script, it looks like this:

__pyarmor__(__name__, __file__, b'\x01\x0a...')

How to Run Obfuscated Script

How to run obfuscated script dist/ by Python Interpreter?

The first 2 lines, which called Bootstrap Code:

from pytransform import pyarmor_runtime

It will fulfil the following tasks

  • Load dynamic library _pytransform by ctypes
  • Check dist/license.lic is valid or not
  • Add 3 cfunctions to module builtins: __pyarmor__, __armor_enter__, __armor_exit__

The next code line in dist/ is:

__pyarmor__(__name__, __file__, b'\x01\x0a...')

__pyarmor__ is called, it will import original module from obfuscated code:

static PyObject *
__pyarmor__(char *name, char *pathname, unsigned char *obfuscated_code)
    char *string_code = restore_obfuscated_code( obfuscated_code );
    PyCodeObject *co = marshal.loads( string_code );
    return PyImport_ExecCodeModuleEx( name, co, pathname );

After that, in the runtime of this python interpreter

  • __armor_enter__ is called as soon as code object is executed, it will restore byte-code of this code object:

    static PyObject *
    __armor_enter__(PyObject *self, PyObject *args)
        // Got code object
        PyFrameObject *frame = PyEval_GetFrame();
        PyCodeObject *f_code = frame->f_code;
        // Increase refcalls of this code object
        // Borrow co_names->ob_refcnt as call counter
        // Generally it will not increased  by Python Interpreter
        PyObject *refcalls = f_code->co_names;
        refcalls->ob_refcnt ++;
        // Restore byte code if it's obfuscated
        if (IS_OBFUSCATED(f_code->co_flags)) {
  • __armor_exit__ is called so long as code object completed execution, it will obfuscate byte-code again:

    static PyObject *
    __armor_exit__(PyObject *self, PyObject *args)
        // Got code object
        PyFrameObject *frame = PyEval_GetFrame();
        PyCodeObject *f_code = frame->f_code;
        // Decrease refcalls of this code object
        PyObject *refcalls = f_code->co_names;
        refcalls->ob_refcnt --;
        // Obfuscate byte code only if this code object isn't used by any function
        // In multi-threads or recursive call, one code object may be referenced
        // by many functions at the same time
        if (refcalls->ob_refcnt == 1) {
        // Clear f_locals in this frame

Special Handling of Entry Script

There are 2 extra changes for entry script:

  • Before obfuscating, insert protection code to entry script.
  • After obfuscated, insert bootstrap code to obfuscated script.

Before obfuscating entry scipt, PyArmor will search the content line by line. If there is line like this:

# {PyArmor Protection Code}

PyArmor will replace this line with protection code.

If there is line like this:

# {No PyArmor Protection Code}

PyArmor will not patch this script.

If both of lines aren’t found, insert protection code before the line:

if __name__ == '__main__'

Do nothing if no __main__ line found.

Here it’s the default template of protection code:

def protect_pytransform():

    import pytransform

    def check_obfuscated_script():
        CO_SIZES = 49, 46, 38, 36
        CO_NAMES = set(['pytransform', 'pyarmor_runtime', '__pyarmor__',
                        '__name__', '__file__'])
        co = pytransform.sys._getframe(3).f_code
        if not ((set(co.co_names) <= CO_NAMES)
                and (len(co.co_code) in CO_SIZES)):
            raise RuntimeError('Unexpected obfuscated script')

    def check_mod_pytransform():
        def _check_co_key(co, v):
            return (len(co.co_names), len(co.co_consts), len(co.co_code)) == v
        for k, (v1, v2, v3) in {keylist}:
            co = getattr(pytransform, k).{code}
            if not _check_co_key(co, v1):
                raise RuntimeError('unexpected')
            if v2:
                if not _check_co_key(co.co_consts[1], v2):
                    raise RuntimeError('unexpected')
            if v3:
                if not _check_co_key(co.{closure}[0].cell_contents.{code}, v3):
                    raise RuntimeError('unexpected')

    def check_lib_pytransform():
        filename = pytransform.os.path.join({rpath}, {filename})
        size = {size}
        n = size >> 2
        with open(filename, 'rb') as f:
            buf =
        fmt = 'I' * n
        checksum = sum(pytransform.struct.unpack(fmt, buf)) & 0xFFFFFFFF
        if not checksum == {checksum}:
            raise RuntimeError("Unexpected %s" % filename)
    except Exception as e:
        print("Protection Fault: %s" % e)


All the string template {xxx} will be replaced with real value by PyArmor.

To prevent PyArmor from inserting this protection code, pass –no-cross-protection as obfuscating the scripts:

pyarmor obfuscate --no-cross-protection

After the entry script is obfuscated, the Bootstrap Code will be inserted at the beginning of the obfuscated script.